In parts of Pennsylvania and New York, the answer to ice-slick wintry roads is simple: Put some gas production waste on it. Municipalities in the northern parts of both states use the salty wastewater from oil and gas production to melt ice in winter and suppress road dust in summer.

The salty liquid does a great job: The brine can be as much as 10 times saltier than typical road salt. Plus it comes cheap; oil and gas companies, glad not to have to pay for disposal, will sell it to towns for cheap, or give it away free. Both states’ environmental protection departments consider brine spreading to be a “beneficial use” of the industrial waste, meaning, in legal terms, that recycling it in this way “does not harm or threaten public health, safety, welfare or the environment.”

But according to new research, the brine is anything but benign. Worse, states barely track it; New York doesn’t know how much of the stuff is being used on its roads, and the Pennsylvania department charged with regulating it appeared to not fully understand its potential effects until Newsweek got in touch.

The wastewater spread on roads comes from oil and gas wells. To drill, production companies send large volumes of water down the well shaft. The water rises back to the surface as a brine laden with chloride (a salt) as well as a number of other constituents like radium and barium, which are radioactive. The brine used on roads comes from conventional oil and gas production, not hydraulic fracturing or “fracking.”

But according to Duke University geochemist Avner Vengosh, the conventional drilling waste is nearly identical in many of its most toxic components to the highly controversial fracking waste. Vengosh says the levels of radioactive material found in conventional brine samples taken from New York are equal to levels he has seen in fracking brine, for example.

What’s more, a study Vengosh and his colleagues published last month in the journal Environmental Science & Technology found that brine being discharged, untreated, into Pennsylvania’s waterways—the same liquid that is spread on roads—also contained significant concentrations of ammonium, iodide and bromide. Each of these chemicals can be toxic to living creatures.

Ammonium, when dissolved in water, is highly toxic to aquatic life. It showed up in samples from discharge sites at levels more than 50 times the U.S. Environmental Protection Agency’s water-quality threshold, according to the study. In other words, as of late summer 2014, when the sampling took place, there was way too much ammonium entering the state’s water bodies.

While the volume of brine used to de-ice roads would be much lower than what was being dumped into rivers, Vengosh says it is important to keep in mind that “you need a very tiny amount of ammonium for it to start to be toxic.”

“No one was much aware of the ammonium.... We were very surprised to find that level in wastewater,” Vengosh says. “If it would be sewage [that was] being released on roads, it would have similar or less ammonium, and it would be criminal to release it like that.”

Iodide and bromide, meanwhile, turn into a variety of toxic compounds when they combine with organic metals in rivers and subsequently flow into water treatment plants, where they combine with the chlorine that gets added to our drinking water during the disinfection process. The interaction with organic metals and chlorine results in “disinfection byproducts”—like iodinated trihalomethanes, brominated trihalomethanes and chloroform—which are carcinogenic.

“It’s kind of sad, perhaps, that in 2015, after decades of operation, we’re just now discovering that [the wastewater] contains those contaminants,” says Vengosh. The problem, he adds, is “that there isn’t any oversight.” He says states need to implement a cap on allowable levels of chloride, the salt component of the brine. Capping chloride levels would effectively limit bromide and iodide levels too, because those constituents always show up in ratios that depend on the amount of chloride in the water.

The first time I called Scott Perry, the deputy secretary for the Pennsylvania Department of Environmental Protection’s (DEP) Office of Oil and Gas Management, he had the opposite take. “We don’t have any data to suggest that that is causing a problem. [Brine spreading] has literally been going on for at least this century and the last,” he says.

Over 3 million gallons of the brine were spread over roads in the northwestern part of the state in 2014. “It doesn’t have to be treated,” Perry says.

A number of other rules must be followed, however. Brine cannot be applied in Pennsylvania within 150 feet of a stream, creek, lake or other body of water, and it can’t be spread while it is raining or “when rain is imminent,” to avoid runoff. If the slope of the road is at an angle steeper than 10 percent, brine can’t be used.

Pennsylvania recently evaluated whether the radioactive material in the brine could have an acute or chronic impact on the health of people who jog or cycle on treated roads and found there was “little potential for harm.” But the study did not look into the implications of brine spreading on the surrounding waterways.

By our second conversation, Perry had dug up a state-funded study from 1996 that gave him pause. The study found that there was, indeed, “potential for brine to migrate from the roadway and impact ground or surface water quality.”

“However, by controlling the frequency and application rates and complying with the other provisions of the DEP guidelines, impacts to ground and surface waters can be minimized while still meeting the road maintenance objective,” the paper reads.

The paper concludes that there is “a need to balance the beneficial aspects of spreading brine on unpaved roads against the potential impacts to ground and surface water.”

Pennsylvania incorporated the recommendations of the study into its brine-spreading guidelines, reducing the volume of the maximum recommended application rate from 1 gallon of brine per square yard of road to half a gallon per square yard. But those remained (and remain today) guidelines for use, not rules.

“I think as a result of my reading that study, and the work we’ve done regarding [radioactivity], it seems to me that it’s really prudent for us to take another look at the use for road spreading,” Perry told me. “I think we should go and take some other samples from the environment. It could result in no changes, that in fact the application rates in the guidelines prove themselves to be correct.

“And I think we should probably look at the effect of chlorides on water resources,” he said.

In New York, meanwhile, even less is known about the brine spreading. A spokeswoman for New York State Department of Environmental Conservation told public radio station WAMC last year that in order to obtain “beneficial use” status in New York, the road-spreading plans must avoid affecting state forest areas, wetlands and surface water bodies. The state reviews permit applications on a case-by-case basis, though the specifics of the requirements are not publicly available.

But the department doesn’t require annual reporting from brine-spreading operations, so it doesn’t know how much is used each year. Plus, brine produced in New York may also be shipped to other states for road spreading, but the department doesn’t track who ships it or where it ends up.

Last year, non-profit water-quality organization Riverkeeper uncovered data about New York brine spreading through a Freedom of Information Law request submitted to the environmental conservation department. They found that permits had been issued to parts of 23 municipalities in seven western New York counties to spread natural gas production brine on roads. FracTracker, a non-profit, turned the data from permits into a map of where the brine is used within the state.

Bill Wegner, a biologist on staff at Riverkeeper, says New York’s safety requirements aren’t enough to protect water supplies. “It can still infiltrate into groundwater, and aquifers, which supply baseflow to streams…[and] I don’t think there’s a safe way to use anything that’s radioactive,” he says. “There are a lot of other ways to de-ice a road.”

Vengosh, meanwhile, says more study needs to be done on the impact of spreading brine on roads. “No one has systematically evaluated this.”

Speaking of his work and that of his colleagues, he says, “We are not anti-fracking at all.” But given how similar toxic wastewater from conventional oil and gas wells is to fracking wastewater, he says, “I see it as the utmost irony that New York banned fracking but allows disposal of brine on roads.”